1. Field of the Invention
The present invention relates to a ferromagnetic amorphous metal alloy; and more particularly to a process for annealing the alloy so that its magnetization curve with respect to applied field becomes linear.
2. Description of the Prior Art
Metallic glasses are metastable materials lacking any long-range order. X-ray diffraction scans of glassy metal alloys show only a diffuse halo similar to that observed for inorganic oxide glasses. Metallic glasses (amorphous metal alloys) have been disclosed in U.S. Pat. No. 3,856,513. These alloys include compositions having the formula MaYbZc, where M is a metal selected from the group consisting of iron, nickel, cobalt, vanadium and chromium, y is an element selected from the group consisting of phosphorous, boron and carbon and Z is an element selected from the group consisting of aluminum, silicon, tin, germanium, indium, antimony and beryllium, xe2x80x9caxe2x80x9d ranges from about 60 to 90 atom percent, xe2x80x9cbxe2x80x9d ranges from about 10 to 30 atom percent and xe2x80x9ccxe2x80x9d ranges from about 0.1 to 15 atom percent. Also disclosed are metallic glass wires having the formula TIXj, where T is at least one transition metal and X is an element selected from the group consisting of phosphorus, boron, carbon, aluminum, silicon, tin, germanium, indium, beryllium and antimony, xe2x80x9cIxe2x80x9d ranges from about 70 to 87 atom percent and xe2x80x9cjxe2x80x9d ranges from 13 to 30 atom percent. Such materials are conveniently prepared by rapid quenching from a melt at temperatures of the order of 1xc3x97106xc2x0 C./sec. using processing techniques that are well known in the art.
These disclosures also mention unusual or unique magnetic properties for many metallic glasses, which fall within the scope of the broad claims. However, metallic glasses possessing a combination of linear BH loop and low losses are required for specific applications such as current/voltage transformers.
A linear B-H characteristic is generally obtained in a soft magnetic material wherein the material""s magnetically easy axis lies perpendicular to the direction of the magnetic excitation. In such a material, the external magnetic field H tends to tilt the average direction of the magnetic flux B, so that the measured quantity B is proportional to H. Most magnetic materials, however, have nonlinear B-H characteristics. As a result, the ideal linear B-H characteristics are not easily achieved. Any deviation from an ideal B-H linearity introduces corresponding deviations in the magnetic response to the externally applied field H.
A classical example of magnetic materials showing linear B-H characteristics is a cold rolled 50% Fexe2x80x94Ni alloy called Isoperm. Among amorphous magnetic alloys, heat-treated Co-rich alloys have been known to provide linear B-H characteristics and are currently used as the magnetic core materials in current transformers. The Co-rich amorphous alloys in general have saturation inductions lower than about 10 kG or 1 Tesla, which limits the maximum field levels to be applied. Moreover, these alloys are expensive owing to the large amount of Co required to form the alloys. Clearly needed are inexpensive alloys having saturation inductions higher than 10 kG and exhibiting linear B-H characteristics.
The present invention provides a method for enhancing the magnetic properties of a metallic glass alloy having in combination a linear BH loop and low core loss. Generally stated, the metallic glasses consist essentially of about 70-87 atom percent iron with up to about 20 atom percent of iron and nickel being replaced by cobalt; up to about 3 atom percent of iron being replaced by at least one of manganese, vanadium, titanium or molybdenum, and about 13-30 atom percent of the elements being selected from the group consisting of boron, silicon and carbon. The method comprises the step of heat-treating the metallic glass alloy for a time and at a temperature sufficient to achieve stress relief and magnetization orientation away from the ribbon axis. In one aspect of the invention, the method is carried out in the absence of a magnetic field. Another aspect of the invention involves the step of carrying out the method in the presence of a magnetic field applied in a direction perpendicular to the ribbon axis.
Metallic glass alloys treated in accordance with the method of this invention are especially suitable for use in devices requiring linear response to magnetic fields, such as current/voltage transformers for metering applications.